Magnetic valves, as used, for example, in the brake circuit of motor vehicles, include a coil for generating a magnetic field by which an armature is actuated. The magnitude of the current flow determines the strength of the magnetic field, in this instance, and with that the setting of the valve (open, closed or intermediate setting). The current flow through the coil is usually set by a valve output stage which includes essentially an output stage switch (MOSFET), which is controlled by drive electronics. The control of the output stage switch takes place mostly by a PWM signal (PWM: pulse width modulation).
During the control of a magnetic valve, for instance, within the scope of an ESP regulation, a heat loss is generated which leads to the heating of the magnetic valve. This raises the ohmic resistance of the valve. Conversely, the magnetic valve cools off when at rest, whereby the resistance goes down as well. Consequently, in a vehicle regulation the problem arises that one and the same PWM signal leads to different valve conditions at various valve temperatures. This impairs the accuracy of the control interventions.
In order to eliminate this problem, it is known, for example, from German Patent No. DE 10 2006 041 193 that one may determine the resistance of a magnetic coil directly via a voltage measurement and readjust the control signal (PWM) of the magnetic valve correspondingly.
However, a resistance measurement is possible only at those times at which the corresponding valve is not being controlled. By contrast, during the control of the valve, the valve temperature and its resistance are not able to be determined.